A regulatory mechanism of muscle contraction based on the flexibility change of the thin filaments

A mechanism for regulation of muscular contraction is proposed on the basis of the finding that a change in flexibility of the thin filaments occurs reversibly at micromolar concentrations of free calcium ions. It is assumed that the volume of muscle is maintained constant during the change of the sarcomere length, and that there is a critical distance between thin and thick filaments for the interaction to generate tension. It is demonstrated by model calculations that both the stretch induced increase of the steady isometric tension at low calcium ion concentrations and the dependence of the rate of tension development on sarcomere length observed by Endo (1972) can be explained by the proposed mechanism.